Geraldine Challoner has been brought up by her two elderly aunts, following the death of her parents in a tornado ten years previously. When her aunts are forced to go abroad she is entrusted to the care of the Trevennors.
Geraldine has been brought up in the style of a girl of the Victorian era, but manages to settle in with the Trevennors and their 10 children. Nell swiftly christens her Gerry and Mrs Trevennor discretely replaces her own clothes with some of her daughter's. Gerry becomes close friends with the oldest boy, Paul, much to the annoyance of his younger sister, Jill.
Gerry is enrolled at St Peter's School where the rest of the Trevennor girls go. She is initiated into the Middle School and quickly settles in. That night Jill appears in Gerry's bedroom and the girls quarrel. The quarrel develops into a physical fight and they are discovered by Paul. This leads to more friction between Jill and Gerry. At school the Middle School decides to strike against the Upper School, and Gerry becomes very involved in this.
Jill is then involved in a skating accident, but is saved by Gerry. The incident leads to Gerry and Jill becoming firm friends, and at school Gerry is delighted to learn that she has gained her remove to IVB.
If you want to find out more, click on Spoilers
As the link suggests, it gives more of the story - without, of course
giving everything away!